Stretchable and Self-Powered Temperature–Pressure Dual Sensing Ionic Skins Based on Thermogalvanic Hydrogels

Abstract

Tactile sensors with both temperature- and pressure-responsive capabilities are critical to enabling future smart artificial intelligence. These sensors can mimic haptic functions of human skin and inevitably suffer from tensile deformation during operation. However, almost all actual multifunctional tactile sensors are either nonstretchable or the sensing signals interfere with each other when stretched. Herein, we propose a stretchable and self-powered temperature–pressure dual functional sensor based on thermogalvanic hydrogels. The sensor operates properly under stretching, which relies on the thermogalvanic effect and constant elastic modulus of hydrogels. The thermogalvanic hydrogel elastomer exhibits an equivalent Seebeck coefficient of −1.21 mV K–1 and a pressure sensitivity of 0.056 kPa–1. Combined with unit array integration, the multifunctional sensor can be used for accurately recording tactile information on human skin and spatial perception. This work provides a conceptual framework and systematic design for stretchable artificial skin, interactive wearables, and smart robots.

Low-Grade Thermal Energy Harvesting and Self-Powered Sensing Based on Thermogalvanic Hydrogels

“…Current research shows that thermogalvanic hydrogel can not only collect heat independently but can also be integrated with other systems to achieve synergistic enhancements. Fu et al proposed a scalable self-powered temperature–pressure dual sensing skin based on thermogalvanic hydrogel (TGHs) [ 124 ], as shown in Figure 19 . TGHs are obtained by introducing the redox coupling agent K 4 [Fe(CN) 6 ]/[K 3 Fe(CN) 6 ] into polyacrylamide hydrogels and, by combining the thermo–current and piezoresistive effects of TGHs, temperature, and pressure stimuli, can be converted into voltage and current signals, thus enabling the simultaneous monitoring of these two indicators.…”

“…All scale bars represent 1 cm. (Reproduced with permission from [ 124 ]. Copyright 2022 American Chemical Society).…”

Recent Development of Self-Powered Tactile Sensors Based on Ionic Hydrogels

“…For the thermogalvanic cell, redox pairs such as Fe(CN /K 3 Fe(CN [ 100 , 101 , 102 ], Fe 3+ /Fe 2+ [ 103 ], I 3− /I − [ 104 ], and SO 2−4 /SO 2−3 [ 105 ] were introduced into ionic hydrogel electrolytes. Application of a temperature gradient across the entire cell leads to a temperature-dependent redox reaction, resulting in oxidation at the anode and reduction at the cathode of the redox couple.…”

“…Fu et al [ 100 ] developed a self-powered temperature–pressure dual-sensing electronic skin based on thermogalvanic hydrogels (TGHs) by introducing the redox couple K 4 Fe(CN) 6 /K 3 Fe(CN) 6 into a polyacrylamide hydrogel ( Figure 15 (bI)). Due to the combination of the thermogalvanic effect and piezoresistive effect of TGH, temperature and pressure stimuli can be converted into voltage and current signals, allowing both parameters to be simultaneously detected.…”

“…TGH sensor array output voltage and relative current change response curves with relaxed and bending states on the human wrist. (Reprinted with permission from [ 100 ]).…”